Thread: 2016 L494 SDV6 HSE - Auxiliary Battery - Part 2 - Charger installation

Very Interesting and useful. Wondering if you can use the spare battery to start the car if the main battery is flat? I know jumper leads would be available but do you have a switch. Also in days of old Battery isolators used to be used which I imagine would not require the charger why did you choose to use a charger?

Thanks Bails

Prefacing the following with "I'm no expert, but..."

The Redarc DCDC charger I'm using is not like a simple isolator (like the Redarc SBI12 for example) in that it does not connect the two batteries together but uses the DC power from the start battery/car charging system to charge the aux. battery.

There is no provision for a switch to connect the two batteries via the DCDC charger - the charger wouldn't be able to handle the cranking current.

I imagine you could install high current cables from the aux. battery to the start battery via a high current relay/solenoid on the +ve and then fit a switch, powered off the aux., which would close the relay/solenoid thereby linking the batteries for starting purposes.

Conceivably you could use jumpers off the aux. directly onto the start battery if you needed to but access to the start battery to do so is not easy given its position under the spare wheel.

Alternatively you'd need a pretty long set of jumpers to reach the jump points under the bonnet from the aux. battery at the back.

A battery isolator like the Redarc one mentioned above is certainly a simpler solution to charging an aux. battery but the research I did revealed I can't use an isolator as the charging system fitted to the car operates by way of a variable voltage alternator.

As I understand it this reduces the output voltage when required (for whatever reason - I don't know why) to an output which would be insufficient to trigger the isolator to close (and link the batteries).

The Redarc isolator requires 13.2V on the charging side to trigger the isolator to link the batteries (and hence start charging your aux.) and will disconnect, isolating the batteries, when the charging side drops to 12.7V.

If the alternator outputs less than 13.2V the isolator won't activate in the first place. If it had triggered, and the alternator reduces its output to 12.7V or less, the isolator will disconnect the aux. which won't then get charged.

I actually had this issue in my previous car (Prado) where I had that isolator fitted. The Prado alternator was (ex-factory) very low output and would not output sufficient voltage to activate the isolator and link the batteries. My aux. was not getting any charge. I had to replace a fuse with a diode to trick the alternator to output a higher voltage which was enough to trigger the isolator and link the batteries.

At the same time I fitted dual voltmeters in the cabin so I could monitor the voltage of both batteries and whether they were linked or isolated. Details here:
Dual Voltmeter Install - PradoPoint - Toyota Prado 4x4 Landcruiser Forum
if anyone's interested. I think it's visible to non-members.

Once I did this the system I fitted to that car worked flawlessly & the isolator did not miss a trick.

I'd certainly recommend the Redarc isolator as a simple dual battery charging solution provided the alternator outputs enough volts to trigger it to link and I did investigate using this on my RRS but it was a no go.

I do recall that someone produces an isolator which is said to work on my current car. I don't have any details but expect it may have lower ON and OFF trigger voltages to cater for a variable voltage alternator.

Cheers

Craig

Have a chat with Tim (user "drivesafe"). He has products designed to work with these vehicles:

Home Page | TRAXIDE - RV | Traxide - RV

Yes, so-called 'smart alternators' cause problems when they cut the power to save running costs.

I've read your first post regarding the battery install and I like the photos.

This and the information you've provided regarding the alternator is going to be useful for future owners.

Just be careful when thinking you have a smart alternator. My 2014 L494 doesn't do any of the fuel saving strategies. It supplies a constant voltage and a standard isolator works fine. You can spend a lot more with these DC-DC chargers and get a worse result.
I recommend monitoring the output voltage and determining if the alternator is "smart" before spending the dollars.

If you want to use a lithium battery it is a different situation, you will need a DC-DC charger for that, regardless of alternator type.

Originally Posted by Geedublya

Just be careful when thinking you have a smart alternator. My 2014 L494 doesn't do any of the fuel saving strategies. It supplies a constant voltage and a standard isolator works fine. You can spend a lot more with these DC-DC chargers and get a worse result.

Originally Posted by Geedublya

I recommend monitoring the output voltage and determining if the alternator is "smart" before spending the dollars.

If you want to use a lithium battery it is a different situation, you will need a DC-DC charger for that, regardless of alternator type.

Hi Craig and with an ordinary lead acid battery, you actually get better results without a DC/DC device, BUT as you went with a DC/DC charge, as Geedublya suggested, why did you use an ordinary battery when a lithium battery would have saved weight and put the DC/DC device to good use?

BTW, that's a nice tray setup.